Fuel cell systems that include a fuel cell in which a fuel gas (e.g., hydrogen) is supplied to a fuel electrode and an oxidizer gas (e.g., air) is supplied to an oxidizer electrode, where the gases electrochemically react with each other to generate electric power are known.
For example, Japanese Unexamined Patent Application Publication No. 7-161371 discloses a method of controlling the temperature of a fuel cell. More specifically, in this method a part of an exhaust gas that has passed through an oxidizer electrode of the fuel cell is mixed with air that is supplied to the oxidizer electrode, and the gas mixture is circulated. In this case, the flow rate of the circulating gas that is discharged from the oxidizer electrode and then circulates is controlled such that the temperature of the gas at the inlet of the oxidizer electrode is kept within a predetermined range. In addition, the flow rate of the air is controlled such that the temperature of the exhaust gas at the outlet of the oxidizer electrode is kept within a predetermined range.
As another example, Japanese Unexamined Patent Application Publication No. 2007-184196 discloses a fuel cell system having a structure in which an unreacted fuel gas discharged from a fuel electrode is mixed with a fuel gas that is supplied to the fuel electrode, and the gas mixture is then circulated.